Back to EveryPatent.com
United States Patent |
5,755,836
|
Beyer
|
May 26, 1998
|
Process for manufacturing a composite fire log and product resulting
therefrom
Abstract
A combustible article consists of agglomerated wood chips and
polyethylene/polypropylene material partially coated with paraffin. The
polyethylene/polypropylene material acts as a fuel as well as a binder;
the paraffin is provided to facilitate lighting. The composite fire log is
produced by combining wood and polyethylene/polypropylene chips or
shavings in a mixer; mixing to produce a substantially uniform aggregate
and heating to a temperature below the melting point of the
polyethylene/polypropylene material; pressing the hot mixture in a press
to form a briquette or fire log of predetermined shape; and dipping the
bottom of the resulting log in molten paraffin.
Inventors:
|
Beyer; Curtis D. (Tucson, AZ)
|
Assignee:
|
Earth Cycle, L.L.C. (Tucson, AZ)
|
Appl. No.:
|
783606 |
Filed:
|
January 14, 1997 |
Current U.S. Class: |
44/535; 44/589; 44/590 |
Intern'l Class: |
C10L 005/06 |
Field of Search: |
44/535,589,590
|
References Cited
U.S. Patent Documents
2015964 | Oct., 1935 | Randall | 44/41.
|
2531828 | Nov., 1950 | Schultz | 158/96.
|
3028228 | Apr., 1962 | Chaplin | 44/14.
|
3227530 | Jan., 1966 | Levelton | 44/1.
|
3852046 | Dec., 1974 | Brown | 44/535.
|
3947255 | Mar., 1976 | Hartman et al. | 44/590.
|
4062655 | Dec., 1977 | Brockbank | 44/6.
|
4243393 | Jan., 1981 | Christian | 44/14.
|
4478601 | Oct., 1984 | Stephens | 44/14.
|
4589887 | May., 1986 | Aunsholt | 44/16.
|
4952216 | Aug., 1990 | Good | 44/535.
|
5342418 | Aug., 1994 | Jesse | 44/589.
|
Primary Examiner: Howard; Jacqueline V.
Attorney, Agent or Firm: Durando; Antonio R.
Claims
I claim:
1. A process for making a combustible article comprising the following
steps:
(a) mixing plant-fiber particles and polyethylene and/or polypropylene
particles to form a substantially uniform mixture;
(b) heating said mixture to a temperature below a flash point of the
mixture; and
(c) pressing the hot mixture resulting from step (b) in a briquette press
at a pressure between 200 and 250 Kg/cm.sup.2 as required to cause
penetration of the polyethylene and/or polypropylene into voids of the
plant-fiber particles.
2. The process recited in claim 1, wherein the plant-fiber particles in
step (a) are mixed in a concentration of between approximately 50 and 90
weight percent of total composition, and the polyethylene and/or
polypropylene particles in a concentration of between approximately 10 and
50 weight percent of total composition.
3. The process recited in claim 1, wherein said plant-fiber particles
comprise material selected from the group consisting of wood, nutshells,
fruit pits, grains, straw, grass, and mixtures thereof.
4. The process recited in claim 1, wherein said plant-fiber particles are
sized to pass through a 50-mm screen.
5. The process recited in claim 1, wherein said polyethylene and/or
polypropylene particles are sized to pass through a 5-mm screen.
6. The process recited in claim 1, wherein said mixture is heated to a
temperature between 150.degree. C. and 200.degree. C.
7. The process recited in claim 1, wherein said plant-fiber particles
comprise material selected from the group consisting of wood, nutshells,
fruit pits, grains, straw, grass, and mixtures thereof; said plant-fiber
particles are sized to pass through a 50-mm screen and said polyethylene
and/or polypropylene particles are sized to pass through a 5-mm screen;
said mixture is heated to a temperature between 150.degree. C. and
200.degree. C.; and said step (c) is carried out at a pressure of about
215 Kg/cm.sup.2.
8. A process for making a combustible article comprising the following
steps:
(a) heating polyethylene and/or polypropylene particles to a temperature
below a flash point of the particles;
(b) heating plant-fiber particles to a temperature below said flash point;
(c) mixing said plant-fiber particles and polyethylene and/or polypropylene
particles to form a substantially uniform mixture; and
(d) pressing the hot mixture resulting from step (c) in a briquette press
at a pressure between 200 and 250 Kg/cm.sup.2 as required to cause
penetration of the polyethylene and/or polypropylene into voids of the
plant-fiber particles.
9. The process recited in claim 1, wherein said step (a) is carried out in
an extruder.
10. A combustible article produced according to the method recited in claim
1.
11. A combustible article produced according to the method recited in claim
8.
12. The process recited in claim 8, wherein the plant-fiber particles in
step (c) are mixed in a concentration of between approximately 50 and 90
weight percent of total composition, and the polyethylene and/or
polypropylene particles in a concentration of between approximately 10 and
50 weight percent of total composition.
13. The process recited in claim 8, wherein said plant-fiber particles
comprise material selected from the group consisting of wood, nutshells,
fruit pits, grains, straw, grass, and mixtures thereof.
14. The process recited in claim 8, wherein said plant-fiber particles are
sized to pass through a 50-mm screen.
15. The process recited in claim 8, wherein said polyethylene and/or
polypropylene particles are sized to pass through a 5-mm screen.
16. The process recited in claim 8, wherein said mixture is heated to a
temperature between 150.degree. C. and 200.degree. C.
17. The process recited in claim 8, wherein said plant-fiber particles
comprise material selected from the group consisting of wood, nutshells,
fruit pits, grains, straw, grass, and mixtures thereof; said plant-fiber
particles are sized to pass through a 50-mm screen and said polyethylene
and/or polypropylene particles are sized to pass through a 5-mm screen;
said mixture is heated to a temperature between 150.degree. C. and
200.degree. C.; and said step (d) is carried out at a pressure of about
215 Kg/cm.sup.2.
18. A combustible article produced according to the method recited in claim
7.
19. A combustible article produced according to the method recited in claim
17.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related in general to fire logs and, in particular, to a
process for manufacturing an aggregate log from particulates of recyclable
materials.
2. Description of the Prior Art
Many commercial fireplace products consist of composites of combustible
materials aggregated into fire logs with binders and other additives to
improve their burning characteristics. Several prior inventions have
included recyclable material in the combustible composition. For example,
U.S. Pat. No. 4,478,601 to Stephens discloses a coal briquette consisting
of coal mine particulates mixed with minor clumps of fibrous wicking
material, a liquid hydrocarbon and methyl cellulose. In one embodiment of
the invention, synthetic polyethylene and polypropylene fibers with
capillary properties are added to the briquette in spaced-apart clumps to
improve its initial burn. The briquette is extruded into a fuel block in a
shape designed to produce burning from inside out with minimal smoke
release.
U.S. Pat. No. 4,243,393 to Christian describes a fire log manufactured by
extruding a mixture of coal particles and a binder. The log features a
hollow core that is at least partially filled with an easily burnable
igniter. Optionally, the log is also dipped in hot wax to facilitate
ignition.
In U.S. Pat. No. 4,589,887, Aunsholt discloses a briquette formed from
biomass material mixed with a fly ash binder. The briquettes are prepared
by extrusion at about 70-110 Kg/cm.sup.2, preferably after preheating to a
temperature of about 50.degree.-70.degree. C.
U.S. Pat. No. 2,531,828 to Schultz teaches a coated fuel-impregnated block
that consists of a liquid fuel absorbed into fibrous material. The
briquette is formed by compressing the absorbent fibrous material, soaking
the resulting block in a liquid fuel, and then immersing the block in a
solution adapted to form an impervious coating to retain the fuel.
Several other patents (U.S. Pat. Nos. 2,015,964, 3,028,228, 3,227,530, and
4,062,655) disclose additional process features and compositions for
improving the performance of fire logs in a fireplace. In view of the
ever-increasing problem of disposal of waste materials, the possibility of
utilizing any recyclable matter in a fire log is both alluring and
sensible. Therefore, some of these prior-art processes have combined
recycled components to conventional fossil fuels to produce a combustible
briquette.
Plastic items returned by individual users to recycling centers in
neighborhood programs throughout the country constitute one of the largest
sources of raw material from recycled matter. A plastic number coding is
utilized to separate categories of plastic according to their chemical
composition, properties, and recyclability. A large portion of these
recycled items consists of high and low density polyethylene (milk/water
jugs, detergent bottles, margarine tubs, bags, yogurt containers)
classified with Codes 2 and 4, for which there are limited recycling
opportunities. Similarly, many items consist of polypropylene
(prescription bottles, plastic lids) classified with Code 5, for which
there are more current recycle uses but are still discarded in large
quantities.
Accordingly, there is still a need for new ways of utilizing recycled high
and low density polyethylene and polypropylene. This disclosure is
directed at a process for utilizing such plastic matter as a major
component of fireplace briquettes or logs.
BRIEF SUMMARY OF THE INVENTION
One objective of this invention is a process for making fire logs utilizing
large quantities of recycled high and low density polyethylene and
polypropylene.
Another goal of the invention is a method of manufacture of fire logs that
is primarily based on the utilization of recycled material.
Still another goal is a process with low energy requirements based on
conventional steps and directed at producing a hot-burning, low-ash,
nearly smoke-free, clean, and efficient fire log.
A final objective is a process that can be implemented easily and
economically with commercially available materials and manufacturing
equipment, modified only to the extent necessary to fit the requirements
of the invention.
Therefore, according to these and other objectives, the present invention
consists of an agglomerate of wood chips and polyethylene and/or
polypropylene material partially coated with paraffin. The plastic
material acts as a fuel as well as a binder; the paraffin is provided to
facilitate lighting, if necessary. The composite fire log is produced by
combining wood and polyethylene/polypropylene chips or shavings in a
mixer; mixing to produce a substantially uniform aggregate and heating to
a temperature below the melting point of the polyethylene/polypropylene
material; pressing the hot mixture in a press to form a briquette or fire
log of predetermined shape; and dipping the bottom of the resulting log in
molten paraffin.
Various other purposes and advantages of the invention will become clear
from its description in the specification that follows and from the novel
features particularly pointed out in the appended claims. Therefore, to
the accomplishment of the objectives described above, this invention
consists of the features hereinafter illustrated in the drawings, fully
described in the detailed description of the preferred embodiment and
particularly pointed out in the claims. However, such drawings and
description disclose but one of the various ways in which the invention
may be practiced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the steps involved in the process
of the invention.
FIG. 2 is a schematic representation of the steps involved in an
alternative process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
This invention is based on the discovery that polyethylene/polypropylene
material uniformly mixed and bonded to wood particles produces a composite
briquette that burns at very high temperature with little production of
smoke and ashes. Contrary to my expectation based on the common perception
that all plastics burn producing unpleasant, apparently toxic, pungent
fumes, and that, therefore, they would not be acceptable as fuels, I
discovered that the process and composition of the invention produce fire
logs with exceptional burn characteristics that enable the commercial
production of fire logs from recycled polyethylenes and polypropylenes.
Based on these results, I developed a product that can be readily produced
entirely from waste materials that have limited other use.
For simplicity, the disclosure below is often presented in terms of
polyethylenes only, but it is understood to be equally applicable to
polypropylenes and to mixtures of the two. Similarly, the disclosed
process temperature ranges were determined to apply to both plastic
components and to mixtures of the two. It is noted that both types of
plastic materials are available in numerous forms with different melting
points and other physical characteristics.
Plant-fiber combustible material and polyethylene/polypropylene are the
only two components critical to the composition of the invention. Sources
of plant fiber can be wood from agricultural waste, byproducts from lumber
mills and other manufacturing operations; nutshells, fruit pits, grains,
straw, and grasses; preferably all recycled from waste and byproduct
sources. Although this disclosure for the most part refers to wood, it is
understood that all such references are intended to include all waste and
byproduct materials that contain combustible plant fiber.
As illustrated schematically in FIG. 1, the process of the invention
involves a step of reducing the wood or other source of carbon (plant
fiber) to chips having a mean particle size of 1 to 50 mm in diameter
(that is, they pass through a 50-mm screen), 20-25 mm being preferred. It
is noted that smaller and larger particles, such as sawdust and wood
chunks, are suitable for the invention but not preferred because of their
poorer burn characteristics. I found that a conventional grinder such as
the Maxigrind 425G manufactured by Rexworks of Milwaukee, Wis., is
suitable for grinding any mixture of these carbon-bearing materials to the
desired size.
The recycled polyethylene/polypropylene material is similarly reduced to
chips or shavings sufficiently small to allow its rapid blending with the
wood material to produce a substantially uniform aggregate. A granulator
such as marketed by Polymer Systems Inc. of Berlin, Conn., as Model
68-912-1116-1120, is suitable for reducing the polyethylene/polypropylene
ma to an acceptable size. The idea is to use small enough particles to
distribute the polyethylene/polypropylene material in the mixture so as to
have great surface contact with the wood particles and maximize the
bonding strength of the aggregate. Particles ground to about 1-5 mm in
effective diameter (that is, ground to pass through a 1- to 5-mm screen)
are optimal for mixing. The ground wood and polyethylene/polypropylene
particles are mixed in conventional equipment, such as plaster or cement
mixers, to yield a uniformly distributed mixture.
The uniform blend of wood and polyethylene/polypropylene particles is then
heated to a temperature below the flash point of the mixture, which I
found to ignite or at least begin smoldering at temperatures below the
melting point of the polyethylene (or polypropylene) at one atmospheric
pressure. The idea of the invention is to form a stable aggregate by
forcing the polyethylene/polypropylene into voids in the wood fiber by
applying sufficient pressure to fluidize the polyethylene/polypropylene at
a temperature below the flash point of the mixture. Thus, the exact
temperature depends on the operating pressure and the exact composition of
the mixture. Typically, a temperature range between 150.degree. C. and
200.degree. C. at about 215 Kg/cm.sup.2 (an average temperature at which
such mixtures begin smoldering at that pressure) is safe for any
wood-source and polyethylene blend, about 160.degree. C. being preferred.
The heating operation is continued until all plastic material has reached
the desired temperature and begun to bond to the surface of wood
particles. This step of the operation can be carried out in a standard
heated mixer or any arrangement suitable for preparing the mixture for
further processing in a press. For example, I heated the mixture with a
hot-air blower while the mixture was being transported on a conveyor to an
auger feeding the press. I found that a mixture based on 10 to 50 percent
by weight of polyethylene/polypropylene (and, correspondingly, on 50-90 wt
% of wood) produces a structurally solid composite without the use of any
binders. This is an advantage of the present invention with respect to
prior-art compositions.
In an alternative method for mixing the wood with the
polyethylene/polypropylene material (particularly suitable for
polyethylene film), the wood particles are heated separately in the mixer,
such as by a hot air flow, and then combined in the mixer with fluidized
polyethylene. This approach is particularly appropriate with low density
polyethylene (recycle Code 4) because that material, being mostly in the
form of thin films, is difficult to grind into discrete particles. In
addition, the lower melting point and ductility of low density
polyethylenes makes it possible to stretch it and blend it even at
atmospheric pressure within the temperature range of operation of the
invention. The separately-heated materials are thus mixed thoroughly to
produce a uniform blend suitable for compaction into a briquette.
Typically, a mixing time of a few minutes is adequate to fully blend the
two components. This approach is illustrated in the diagram of FIG. 2.
If heavier polyethylenes or polypropylenes are used, the step of heating
the plastic particles in the process of FIG. 2 can advantageously be
carried out in an extruder under pressure where the relative absence of
air in the extruder makes it possible to heat the plastic material to
temperatures as high as 230.degree. C. without flashing. The balance of
the process is then carried out by blending the extruded plastic and the
heated wood as described above.
The hot mixture so obtained is then processed in a conventional briquette
press to concretely bond the particles of the mixture and, at the same
time, to produce fire logs. This compaction step is carried out at a
pressure of about 2,800 to 3,500 pounds per square inch (about 200 to 250
Kg/cm.sup.2). At these high pressures the hot polyethylene/polypropylene
is partially fluidized and forced to permeate or penetrate into voids in
the wood fibers and the high level of compaction (typically the volume of
the aggregate is halved in the press) produces a uniformly bonded
composite that requires no other binding agent. The exact compaction
pressure is selected with a view to producing a concrete and stable
aggregate with sufficient porosity to sustain burning throughout the log.
For a mixture containing about 83 weight percent wood fiber, a pressure of
about 3,000 psi (approximately 215 Kg/cm.sup.2) is optimal.
Ventilation holes are preferably formed in the logs during the compaction
step or drilled into them at a later time. Finally, in order to facilitate
the initial ignition of the log, its lower portion can be immersed in
liquid paraffin (which is also available as recycled material) or other
wax with a low ignition temperature and be allowed to absorb a sufficient
amount to produce a self-sustaining flame. I found that 2 to 16 ounces of
paraffin (preferably 4 ounces) distributed over an outer layer are
adequate for a 12-lb mass of aggregate shaped into a log approximately 16
inches long, 6 inches wide and 6 inches high.
The resulting log burns longer and hotter than a comparable wood log. It
produces approximately 11,000 Btu/lb, which is comparable to bituminous
fuels. By contrast, though, the logs of my invention leave no unburned
chunks, which are typical of wood and coal; rather, they produce only
powder ashes. The logs do not produce sparks and burn well mixed with
other fuels, such as firewood or coal.
Moreover, the logs of the invention have been measured to produce less than
25% of the particulate matter (smoke), carbon monoxide, polycyclic
aromatic hydrocarbons, and formaldehyde emitted by firewood. Although the
reasons for this improvement are not specifically understood, I believe
that they derive from the relatively higher flame temperature that the
wood/polyethylene composites produce.
The fire logs of the invention are preferably packaged in cardboard boxes
for ease of handling, storage and transportation. Because of the ease of
ignition provided by the paraffin layer, the logs can be burned without
first removing them from their box, which greatly facilitates the process
of using them in a fireplace.
Thus, one advantage of this invention is the simplicity of the process
through which an efficient, hot-burning fire log is manufactured utilizing
primarily recycled materials. By applying sufficient pressure to the
mixture in the press to achieve partial permeation of the
polyethylene/polypropylene material into the wood fiber at safe
temperatures (below the flash point of the mixture), no binders or other
additives are required to yield an acceptably strong composite. Instead,
because of the process by which the logs are manufactured, one of the fuel
components itself (polyethylene/polypropylene) provides the necessary
binding. Another advantage of the invention is derived from the unexpected
burning characteristics of the wood/polyethylene mixture, which provide an
efficient and environmentally sound source of fuel.
The following examples illustrate the process and product of the invention.
EXAMPLE 1
A batch of about 130 pounds of scrap wood pieces were ground to less then
25-mm particles. A batch of about 27 pounds of recycled polyethylene
(mostly from water and milk bottles) was ground into particles smaller
than 5 mm. The two batches were mixed in a plaster mixer (83 wt % wood, 17
wt % polyethylene) for about one minute to produce a substantially uniform
blend. The composite mixture was then heated to approximately 160 degrees
centigrade with hot air and fed to a press through an auger. The press was
operated at approximately 215 Kg/cm.sup.2 to form a fire log. The bottom
portion of the log was then dipped in molten paraffin.
EXAMPLE 2
A 140-lb batch of a mixture of scrap wood pieces and nutshells (60%
wood/40% nutshell weight ratio) were ground to less then 25-mm particles.
A 30-lb batch of recycled polyethylene (mostly from water and milk
bottles) was ground into particles smaller than 5 mm. The two batches were
mixed (82 wt % wood/nutshell, 18 wt % polyethylene) in a plaster mixer for
about one minute to produce a substantially uniform blend. The composite
mixture was then heated to approximately 160 degrees centigrade with hot
air and fed to a press through an auger. The press was operated at
approximately 230 Kg/cm.sup.2 to form a fire log. The bottom portion of
the log was then dipped in molten paraffin.
EXAMPLE 3
About 140 lbs of a sawdust were mixed with a 30-lb batch of recycled
polyethylene (mostly from water and milk bottles) in particles smaller
than 5 mm. The two batches components were mixed (82 wt % sawdust, 18 wt %
polyethylene) in a plaster mixer for about one minute to produce a
substantially uniform blend. The composite mixture was then heated to
approximately 160 degrees centigrade with hot air and fed to a press
through an auger. The press was operated at approximately 230 Kg/cm.sup.2
to form a fire log. The bottom portion of the log was then dipped in
molten paraffin. Vertical ventilation holes were drilled in the log.
Various changes in the details, steps and materials that have been
described may be made by those skilled in the art within the principles
and scope of the invention herein illustrated and defined in the appended
claims. Therefore, while the present invention has been shown and
described herein in what is believed to be the most practical and
preferred embodiments, it is recognized that departures can be made
therefrom within the scope of the invention, which is not to be limited to
the details disclosed herein but is to be accorded the full scope of the
claims so as to embrace any and all equivalent processes and products.
Top